Photographic light-sensitive material and process of making the same



Patented July 31, 1928.

UNITED STATES 1,678,832 PATENT OFFICE.

SAMUEL E. SHEPPARD, OF ROCHESTER, NEW YORK, ASSIGNOR T EASTMAN KODAKCOMPANY, OF ROCHESTER, NEW YORK, A. CORPORATION OF NEW YORK.

PHOTOGRAPHIC LIGHT-SENSITIVE MATERIAL AND PROCESS OF MAKING THE SAME.

No Drawing.

This invention relates to the art of photographic light-sensitivematerials and to processes of preparing such materials. One object ofthe invention is to provide photographic emulsions having improvedproperties because of the presence therein of certain sensitizingsubstances which I have discovered. Another object of the invention isto provide processes in which such sensltlzing substances are used toimprove the hghtsensitiveness of photographic emulsions, articularlydeveloping-out ones. A still urther object of the inventon is to providecolloid products, such as gelatins, the ability of which to formlight-sensitive photographic emulsions is greatly increased by saidsensitizing substances. Another object of the invention is to provideprocesses for preparing said colloid products. Other objects willhereinafter appear.

In my U. S. Patent No. 1,574,944, March 2nd, 1926 for photographiclight-sensitive material and process of making the same, I havedisclosed, among other things, a class of sensitizing materials by meansof which the light-sensitiveness of photographic emulsions can begreatly increased, and by means of which colloids, such as gelatins, canbe put into the best condition for manufacturing such emulsions. Suchmaterials are effective even when used in very minute quantitiesrelative to the other ingredients of the emulsion.

I have now found another class of sensitizing substances which aresimilarly effective in the production of light-sensitive emulsions andin the preparation of colloidal intermediates for the manufacture ofsuch emulsions. This new class includes all of the disulfids indicatedby the formula,

Application filed June 6, 1927. Serial No. 196.992.

One example of such a substance is the salt of ethyl dioxythiocarbonateas prepared by Debus (Liebigs Anualendcr Ohemie, Vol. 72, page 1 andVol. 75, page 121) Other examples are the compounds obtained by theaction of bromine on mustard oils, or isothiocyanates. These aresometimes called mustard oil oxides. (See Freund, Liebigs AnnalenderOhemie, Vol. 235, page 14.)

Still other examples are the thiurets having the following formula,-

s-s RN==C d=NH Another illustration is benzoyldisulfide:

OqHg-C-S-S-C-CBHE a a The proportions in which these compounds areincorporated in the emulsions, or in the colloids for the emulsions, areimportant. Too much of them will cause fog. The, maximum proportionswhich can be used practically vary slightly with the particularsensitizing compound which is selected, with the ratio of gelatin tosilver halide in the emulsion, with the type of emulslon, as regardsgrain size, and alkalinlty, with the amount of natural sensitizer alsopresent in the gelatin when the latter is manufactured, with theparticular silver halide or halides employed, and with the fog standardswhich are set by the emulsion maker. The maximum proportion in any caseis readily found by routine test.

In all cases the proportion of the sensitizmg compound relative to theother ingredients of the emulsion is remarkably minute. Withgelatino-silver-halide developing-out emulsions it is generally lessthan about ten grains of active sensitizing compound in 130 7 pounds ofemulsion (the latter being computd as the weight of its non-equeousingredients in the dry state); or less than about ten grains in 100pounds of gelatin (computed as dry gelatin). Smaller proportions arevery useful, such as two to three grains of the sensitizing, compound to100 pounds of dry gelatin or 130 pounds of emulsion.

It will be noted that the quantities of sensitizing compounds are sosmall in the gelatins or emulsions, that they do not appreciably dilutethem, nor have any effect upon their physical properties. Thephotographic colloids, such as gelatins, can be selected so as to havethe right physical properties, such as setting ability, viscosity andproper melting point, without worrying about whether they have alsosuflicient lightsensitizing power. The latter can be brought up to thenormally useful degree by adding my sensitizing compounds. This enablesme to cstablish'a ratio of sensitizing compounds to the silver halide inthe emulsions which is independent of the ratio of the gelatin to saidsilver halides.

Like the sensitizing compounds described in my above mentioned patent,the present sensitizing compounds are chemical sensitizers whlchincrease the general sensitiveness of the photographic emulsions unlikethe effects of dyes which optically sensitize the emulsions to increasetheir sensitiveness to some particular narrow group of wave lengths. Mypresent sensitizing compounds are effective in all, kinds of emulsionsordinarily met with, such as orthochromatic, panchromatic, X-ray, aswell as the ordinary non-color-sensitized ones. They can be addedwithout or with sensitizing dyes or before or after them.

My present sensitizing substances may be, in general, incorporated inthe emulsions or in the colloids for the emulsions in the same way asthose set forth in my above cited patent. For example, a mixed silverbromide and iodide emulsion in gelatin may be prepared, as set forth inpage 3 of said Patent No. 1,574,944. After the emulsion is prepared itmay be melted and the proper amount of sensitizing compound thoroughlymixed into it. This mixing is conveniently elfected by dissolving thesensitizing substance in ethyl alcohol or water or a mixture of them,and then stirring such solution into the emulsion. I find it goodpractice to keep the volume of the solution of sensitizcr below about 2%of the volume of the emulsion into which it is mixed. Where, forinstance, one part of benzoyldisulfide by weight is to be incorporatedinto about 300,000 parts by weight of such emulsion (computed as theweight of its non-aqueous ingredients), the benzoyldisulfide isdissolved in a slightly aqueous ethyl alcohol, equal in volume to 1.5%of the emulsion, and is then stirred into the latter while melted.

Instead of incorporating -n1y sensitized compounds into the meltedemulsion, they may be premixed with the emulsion-forming colloid, suchas gelatin. In general there is added to the gelatin enough of mysensitizing compounds to make up for any deficiency of naturalsensitizing compounds in said gelatin. I may even employ gelatin whichis free from natural sensitizing substances, and

depend upon my added sensitized compounds to give it the power to formhighly lightsensitive photographic emulsions. In this way I prepare thecolloid in a form which serves as a valuable intermediate in thereparation of photographic emulsions. *or example, I may dissolve two orthree grains of benzoyldisulfide in slightly aqueous alcohol, andcarefully stir the solution into 100 parts of melted gelatin (calculatedas dry gelatin). The volume of the alcoholic solution should be onlyabout 1.5% of the volume of the gelatin, thus avoiding anyv appreciabledilution of the colloid.

lVhere it is desired, for simplicity in manufacture, to render gelatininert and then add known amounts of sensitizing compounds to it, thegelatin may be treated with oxidizing agents, as set forth in page 5 ofmy Patent No. 1,574,944. This destroys the natural sensitizing compoundspresent in the gelatin. Then, after proper washing of the gelatin, theright proportions of my sensitizing compounds may be added, as indicatedabove.

When my new sensitizing compounds are added either to the emulsion, orto colloids for making the emulsion, as hereinabove described, there isan advantage in maintaining a slightly acid condition until a thoroughmixture has been obtained, my new substances having less tendency toprematurel split oif sulfur, under such conditions. f course, thealkalinity of the emulsion is immediately restored, as will beunderstood by those skilled in this art.

While my novel sensitizing compounds are preferably used with gelatin,they, nevertheless, have utility with emulsions made in other colloids,such as albumens, agar-agar, gums, like gum arabic, and cellulosicderivatives. My compounds likewise have utility in emulsions in whichdifferent kinds of silver salts are present, such as silver bromide,silver iodide, silver chlorid, or mixtures of any of these with one ormore of the others. In place of the above described disulfids, there maybe substituted the corresponding diselenids or ditellurids whichfunction as sensitizing compounds in the same way. When I referhereinafter to disulfids it will be understood that I include suchequivalents.

Having thus described my invention, what I claim asnew and desire tosecure by LettersPatent is: I

1. A photographic emulsion comprising a colloid, particles ofphotographic silver salts suspended therein, and an added compoundtherein upon which at least part of the light-sensitiveness of theemulsion depends, said compound being a disulfide of the typeR-o-s-s-o-R a in which R is any organic radical and X and Y are selectedfrom the group of oxygen, imid-nitrogen, sulfur, double bonded carbon.

2. A photographic developing-out gelatino-silver halide emulsion of thealkaline type of relatively high light-sensitiveness, comprising amixture of the constituents of a gelatino-silver-halide emulsion oflower light-sensitiveness, and an added sensitizing compound upon whichdepends the difference between said lower and said highlightsensitiveness, said compound being a disulfide of the type in whichR is any organic radical and X and Y are selected from the group ofoxygen, imid-nitrogen, sulfur, double bonded carbon;

3. A photographic emulsion comprising a colloid, particles ofphotographic silver salt suspended therein and an added compound thereinupon which at least part sensitiveness of the emulsion depends, saidcompound being less than the order of ten grains per 130 pounds ofemulsion, being insufficient to cause immediate fogging tendency, and.being a disulfide of the type RCS-SO R ll ll X Y in which R-is anyorganic radical and X and Y are selected from the group of oxygen,imid-nitrogen, sulfur, double bonded carbon.

4. In" the process of ing-out colloid sensitive-silver salt emulsion,increasing the light-sensitiveness thereof by incorporating with theother constituents thereof a disulfide of the type in which R is anyorganic radical and X and Y are selected from the group of oxygen,imid-nitrogen, sulfur, double bonded carbon. r

5. In the process of preparing :1 developing-outcolloid-sensitive-silver-salt emulsion, increasing thelight-sensitiveness thereof by incorporating with the other constituentsthereof an independent sensitizing compound in proportions less than theorder of ten grains of compound per 130 pounds of emulsion,

' photographic of the lightpreparing a developbeing a disulfide of thetype I R-C-S-S-C-R I I x Y emulsion.

7. An intermediate for use in making emulsions, emulsion-forming colloidhaving incorporated therein, a disufide of the type R-c-s-s-o-R I U x Yin which R is any and .Y are selected gen, imid-nitrogen, carbon.

8. The process of making an intermediate for use in the preparation ofphotographic emulsions, which comprises incorporating in anemulsion-forming colloid a disulfide of the type organic radical and Xfrom the group of oxysulfur, double bonded ll X Y in which R is anyorganic radical and X- and Y are selected from the i group of oxygen,lmld-nitrogen, sulfur, double bonded carbon.

Signed at Rochester, New York, this 28th day of May, 1927.

SAMUEL E. SHEPPARD.

comprising an said compound being insuflicient to cause immediatefogging tendency, and

